Sounding reference signals (SRS) are transmitted on an uplink channel between a mobile terminal and a base station so as to allow the base station to estimate the quality of the uplink channel at different frequencies. Based upon the estimates of the quality of the uplink channel, the network may schedule uplink transmissions on resource blocks having good quality.
SRS are configured based upon a number of parameters. For example, the configuration of the SRS in LTE release 8 is described in the corresponding physical layer specification, that is, 3GPP TS 36.211. For example, the configuration of the SRS may be defined by parameters such as the cell-specific SRS bandwidth CSRS, the mobile terminal-specific SRS bandwidth BSRS, the mobile terminal-specific cyclic shift for SRS sequence NSRScs, the mobile terminal-specific SRS transmission comb kTC and the SRS sequence length Msc,brs. As defined by 3GPP TS 36.211, for example, CSRS may be an element of {0,1,2,3,4,5,6,7}, BSRS may be an element of {0,1,2,3}, NSRScs may equal 0,1,2,3,4,5,6 or 7, kTC may be an element of {0,1} and Msc,brs may be set equal to (mSRS,bNxcrb)/2. Many of these parameters may be configured in a higher layer to be either cell-specific or mobile terminal-specific.
Based upon these parameters, a mobile terminal may determine the assigned SRS resource with the frequency starting point and the physical resources into which the CRS shall be mapped being a function of these parameters. For example, in an instance in which the uplink bandwidth NulRB is equal to or between 6 and 40, that is, 6≦NulRB≦40, mSRS,b and Nb may be defined based upon the cell-specific SRS bandwidth and the mobile terminal-specific SRS bandwidth as follows for values at B=0,1,2 and 3:
SRSSRS-SRS-SRS-SRS-bandwidthBandwidthBandwidthBandwidthBandwidthconfigurationBSRS = 0BSRS = 1BSRS = 2BSRS = 3CSRSmSRS, 0N0mSRS, 1N1mSRS, 2N2mSRS, 3N303611234341132116282422241464141320145414141614441415121434141681424141741414141
These parameters, that is, mSRS,b and Nb, are defined, for example, by 3GPP TS 36.211, v9.0.0, section 5.5.3.2 with mSRS,b being a value that is utilized to calculate the actual bandwidth for the SRS signal in terms of the number of subcarriers and Nb being a value that determines the number of possible SRS frequency domain starting positions exist for a given SRS transmission bandwidth mSRS,b.
SRS resources may be arranged in a tree structure. For example, in releases 8, 9 and 10 of LTE, SRS resources are arranged in a tree structure as may be observed from the definition of the frequency starting position k0 for a given set of SRS resources without SRS frequency hopping as follows:
      k    0    =            k      0      ′        +                  ∑                  b          =          0                          B          SRS                    ⁢                          ⁢              2        ⁢                  M                      sc            ,            b                    RS                ⁢                  n          b                    where for normal uplink subframes k0′=(└NRBUL/2┘−mSRS,0/2)NSCRB+kTC In this context, a normal uplink subframe is an uplink subframe other than a special uplink subframe as described, for example, by 3GPP TS 36.211, v9.0.0, section 4.2.
By way of example, FIG. 1 illustrates the SRS resources of a mobile terminal in which the cell-specific SRS bandwidth is 36 physical resource blocks (PRBs). In this regard, the SRS resources of a mobile terminal are determined based on the cell-specific SRS bandwidth, the mobile terminal-specific SRS bandwidth and a frequency starting position, which may be a function of a mobile terminal-specific offset that is configured at a higher layer. In FIG. 1, for example, there are 1, 3 and 9 resources for SRS bandwidths of 36, 12 and 4 PRBs, respectively. In the example of FIG. 1, PRBs are also reserved at the opposite bandwidth edges, such as two PRBs being positioned at each bandwidth edge that may be used, for example, for physical uplink control channel (PUCCH) signaling.
In an instance involving carrier aggregation, SRS may be provided for a component carrier (CC). In this regard, carrier aggregation is a combination of two or more component carriers operating at different frequencies in order to provide a broader transmission bandwidth for a mobile terminal. The component carriers aggregated in accordance with carrier aggregation may include a primary component carrier and one or more secondary component carriers. The primary component carrier may be that which: (i) operates on a primary carrier in which the mobile terminal either performs the initial connection establishment procedure or initiates the connection re-establishment procedure, or (ii) was indicated as a primary component carrier in a handover procedure. Conversely, a secondary component carrier, operating on a secondary carrier, may be that which is configured once radio resource control (RRC) is established and which may be used to provide additional radio resources.
At least some component carriers may be backwards compatible. For example, a backwards compatible component carrier of release 10 or 11 of LTE has the same bandwidth, such as 5 MHz, as the component carriers of a prior version, such as releases 8 or 9 of LTE. In some instances, however, the bandwidth that is required for transmission does not closely match the bandwidth of the backwards compatible component carrier. For example, the bandwidth that is required for transmission may be slightly larger than the bandwidth of the backwards compatible component carrier. While multiple component carriers may be aggregated to support the transmission, the aggregation of the component carriers may result in the dedication of excessive bandwidth to the transmission. Alternatively, the component carriers may be sized to have different bandwidths that more closely match the transmission, but the component carriers would then no longer be backwards compatible.
As such, segment carriers have been proposed. A segment carrier is a contiguous bandwidth extension of a backwards compatible component carrier. Thus, in the instance in which the bandwidth required for transmission is slightly larger than the bandwidth of a backwards compatible component carrier, the transmission may be supported by a combination of the backwards compatible component carrier and a segment carrier that is appended to and contiguous with the component carrier from a bandwidth perspective. As such, segment carriers provide for efficient transmission even in instances in which the bandwidth required for transmission differs from the bandwidth of the backwards compatible component carriers, while permitting the component carriers to remain backwards compatible. Moreover, segment carriers may provide for efficient signal transmission in that a segment carrier and the backwards compatible component carrier from which the segment carrier extends share a single physical downlink control channel (PDCCH) for resource allocation and a signal hybrid authorization request (HARQ) for the combined bandwidth.
However, SRS has not been provided for segment carriers. Since the bandwidth of a segment carrier may be significant and/or since the channel fading characteristics may be quite different for a frequency selective channel even when spaced a few PRBs away from the component carrier, it may be advisable to also provide SRS for a segment carrier.